1. Field of Invention
This invention relates generally to the field of fastening devices and methods of use, and more particularly to threaded fasteners and thread clamping devices having improved locking characteristics in the ratcheting direction.
2. Description of the Prior Art
Wood is a major construction material in many places throughout the world. Wooden structures frequently use “tie-downs” to secure the wooden structure to its foundation, typically a concrete foundation or a concrete and block foundation. The function of tie-downs is thus to secure the wooden structure to its foundation in the presence of forces (perhaps substantial forces) tending to separate the structure from its foundation, such as high winds, seismic events or general shifting and settling of the surrounding earth. However, the wood typically used for construction often has considerable water content when initially installed and with time, the water evaporates and the wood dries out. In the process of drying out, the wood dimensionally shrinks. Approximately 4% shrinkage in the first year following construction of a wooden structure is not uncommon.
This shrinkage commonly causes tie-downs to loosen, thereby making the structure more susceptible to damaging displacements in the presence of high winds, earthquakes among other external forces. Catastrophic damage may result.
A common method for implementing a tie-down is by imbedding a vertical threaded rod into the concrete of the foundation at the location where the wooden structure is to be joined to the foundation. The threaded rod generally resides within the walls of a single or multilevel structure as it passes from the concrete foundation up through each floor of the structure. Each floor is typically attached to the threaded rod by a separate tie-down. The primary fastener presently used to implement a tie-down is a standard “hex” nut.
If a standard nut is used, a space will typically develop under the standard nut and above the wood as the wood shrinks in dimension due to loss of water as described above. This space allows the tie-down (and structure) to move vertically when an overturning moment is applied to the structure as might occur, for example, during a seismic event, wind loading, among other circumstances. This motion of the structure with respect to the foundation, in turn, allows for deformation of the structural walls and may produce substantial damage that the tie-down is designed to prevent when functioning properly, that is when holding the structure securely in place on the foundation. Thus, a need exists in the art for a tie-down that is self-compensating, that is, a tie-down that maintains secure attachment of the structure to the foundation despite shrinkage of the wood.
The International Codes Council (“ICC”) has recently adopted Acceptance Criteria (“AC”), AC316, that require Tension Controlled Shrinkage Compensation Devices (“TCSCD”) to meet certain performance criteria. Among these is a requirement that the deflection of the TCSCD under load is limited to 0.125 inch minus “looseness.” “Looseness” as used in this AC is defined as the distance the threaded rod must be moved in the locking direction relative to the TCD before the TCD segments lock to the rod.
Receiving formal ICC approval for a device is an important commercial advantage in the US market. But ICC approval is based upon successfully passing independent performance tests and evaluations, providing strong evidence of the devices' capabilities, even in those locations in which formal ICC approval is not called for. Thus, a need exists in the art for a TCD meeting ICC AC, and also demonstrating improved overall performance.